Jem 2100 electron microscopy

The morphology of collagen fibrils was observed using scanning electron microscope (SEM; S4800, Hitachi, Tokyo, Japan) according to the procedures described by Ran et al. (2020) [16 (link)]. Collagen stock solutions (1 mg/mL) were prepared as described in Section 3.2, and 50 μL of collagen stock solutions were incubated overnight at 30 °C in clean slides. The treated samples were rinsed carefully with deionized water for several times and fixed with 2.5% (v/v) glutaraldehyde for 2 h, then dehydrated with 50% (v/v) ethanol and freeze-drying with a freeze dryer (SCIENTZ-10ND, Ningbo Xinzhi Biotechnology Co. ltd., Ningbo, China). The dried samples were observed by SEM at an accelerating voltage of 5 kV, and the diameters of 100 fibrils were analyzed with ImageJ software (v1.51, National Institutes of Health, Bethesda, MD, USA).
Observation of the collagen fibrils by transmission electron microscopy (TEM) were performed according to the method of Liu et al. (2014) [29 (link)] with slight modifications. Collagen stock solutions were prepared the same as Section 3.2. One drop of the solution was loaded on a copper grid with 200 mesh size and stained with 1% (w/v) phosphotungstic acid, and then then washed with deionized water and air dried. The collagen fibrils were observed using a JEM-2100 electron microscopy (JEOL Ltd., Tokyo, Japan) with an accelerating voltage of 200 kV.

Powder X-ray diffraction (XRD) was performed on a Bruker D8-Advance diffractometer using monochromatized Cu Kα (λ = 0.15418 nm) radiation with scanning speed of 3°/min. A field emission scanning electron microscope (JSM-7001F, JEOL) operating at a 5 kV was used to characterize the morphology of the samples. The transmission electron microscopic (TEM) images were collected with a JEOL JEM-2100 electron microscopy at an acceleration voltage of 200 kV. UV-Vis-NIR diffuser reflectance (DRS) measurements were carried out on UV/Vis/NIR spectrometer (PerkinElmer, Lambda 950). Fourier transform infrared spectroscopy (FTIR) of the samples was recorded on a Fourier Transform Infrared Spectrometer (VERTEX 70 V, Bruker).

The crystalline phases of as-prepared samples were characterized by X-ray powder diffraction (XRD) on Bruker D2 X-ray diffractomer using Cu K_α radiation (λ = 1.5418 Å). The morphology and chemical composition of the samples were characterized by scanning electron microscopy (SEM, Hitachi SU 8010) attached with energy dispersive X-ray Spectroscope (EDS), and element mapping was also taken for the chemical analysis of the sample. The microstructures were also observed by a transmission electron microscopy (TEM) on the JEM-2100 electron microscopy (JEOL, Japan) with an accelerating voltage 200 kV. The actual Gd doping contents of as-prepared photocatalysts were determined using inductively coupled plasma mass spectrometry (ICP-MS, PE NexION 300X). The chemical states of the prepared samples were investigated by using X-ray photoelectron spectroscopy (XPS). The spectra were recorded on a PHI 5000 Versa Probe with Al K_α radiation. Ultraviolet-visible (UV-vis) diffuse reflectance spectra (DRS) of the samples were recorded on a Shimadzu UV-3600 in the wavelength range of 200 ~ 800 nm equipped with an integrating sphere, and BaSO₄ was used as a reflectance standard. The photoluminescence (PL) measurements were recorded on a Hitachi High-Tech F-7000 fluorescence spectrophotometer with a xenon lamp at the excitation wavelength of 400 nm.